An active suspension system for a motor vehicle utilizes actuable struts at each wheel of the vehicle whereby the pressure within the struts may be controlled to actively regulate the damping and spring effect of the suspension system. One key component of such an active suspension system is a pressure detector or sensor that provides a reading of the strut mean pressure for each strut. As used herein, the strut mean pressure is the static pressure variation a strut can have after executing flow demands.
Typically, a high level vehicle dynamics controller creates a desired pressure for a particular strut, and based on a comparison between the detected strut mean pressure and the desired pressure, an actuator increases or decreases the pressure within the strut to meet the desired pressure level. It can therefore be seen that the pressure sensor is a very important component of the active suspension system.
When a strut is exposed to payload, vibration and the execution of flow demands, the strut pressure is composed of payload-dependent pressure (i.e. precharged pressure), vibration-dependent pressure, and pulsation-dependent pressure. Additionally, the strut load also includes friction due to vibration. Unfortunately, all of these pressure components are not desirable from the standpoint of controlling the pressure within the strut. Specifically, if a pressure sensor is used, the control algorithm needs to include a complicated estimation algorithm to figure out the achieved controllable pressure when a flow demand is executed. The complicated estimation algorithm must factor out certain pressure components such as those previously mentioned.
Accordingly, there exist a need to provide a method and apparatus for estimating the strut mean pressure in a strut forming a portion of an active suspension system, the method and apparatus eliminating the need for a costly pressure sensor and the complicated estimation algorithm which are required to determine the achieved controllable pressure.